Finally genes have been identified that may help predict outcomes for naltrexone treatment for alcohol dependence, such as the A118G OPRM1 single-nucleotide polymorphism (SNP) (Enoch 2013) and for response to nicotine replacement therapy for smoking cessation, such as the D398N SNP in the α5 gene and CYP2A6 genetic polymorphisms (Chen et al. 2014a,b). Here, OPRM1 is linked to alcohol dependence.